1. The problem statement, all variables and given/known data A smooth vertical tube having two different sections is open from both ends equipped with two pistons of different areas figure. Each piston slides within a respective tube section. One mole of ideal gas is enclosed between the pistons tied with a nonstretchable thread. The cross-sectional area of the upper piston is ΔS greater than that of the lower one. The combined mass of the two pistons is equal to m. The outside air pressure is P0. By how many Kelvin’s must the gas between the pistons be heated to shift the pistons through l? 2. Relevant equations http://www.luiseduardo.com.br/mechanics/liquids/liquidsproblems_arquivos/image028.jpg [Broken] 3. The attempt at a solution Pressure of gas present inside = P0 + mg/ΔS I have a doubt regarding the pressure of the gas. Will it remain the same throughout the expansion? If yes, why?